The present invention relates to pressure line instrumentation, and more particularly to safety valve set pressure measuring devices.
In the prior art, pressure lines are often designed with safety valves located at various positions along their length. The conventional valves, such as the Type HB Valves, manufactured by Crosby Valve and Gage Company, Wrentham, Mass., include a closure element which is nominally biased against the port to seal the port. Typically, this bias is provided by a springloaded assembly coupled to the closure element. The safety valve is designed so that when the pressure in the line is below a predetermined threshold, defined as the set pressure, the valve port is sealed. However, when the pressure within the line exceeds the set pressure, the line pressure is sufficient to overcome the spring bias so that the valve lifts from its seating in the valve port and the medium within the pressure line may freely escape. In the prior art, safety valves are designed for specifically desired set pressures for various applications.
One problem in the use of such safety valves is the need to ensure that the set pressure for a valve, as installed, does not change with time, or, if the set point does change, this change may be measured. In general, the set points for safety valves are periodically tested. In one approach to measuring set points, the valve is removed from the pressure line assembly, fitted to a test jig, tested for set point, and then reinstalled or replaced as necessary. This approach, of course, necessitates a shutdown of the pressure line during set point testing.
In an alternative approach known in the art, a valve may be fitted with an air-operated lifting motor (in the form of a diaphram sealed, air cylinder having a known effective area) coupled to the closure element, and a pressure gauge. In operation, a test operator applies air pressure to the air motor by way of an air pressure regulator or a manual control valve. The resultant force from the motor is applied to the closure element to lift the closure element against the springloaded bias. When the lifting force from the motor together with the force from the pressure within the line is sufficient to overcome the springloaded bias force, the closure element lifts off its seat, accompanied by an audible leak (or "pop"). When the "pop" is detected by the operator, the air pressure applied to the air motor is measured, and a differential force value may be derived from a predetermined relationship between those parameters for the valve. This differential pressure may be added to the pressure within the line to yield the set pressure characteristic for the valve.
While the audible "pop" which accompanies the lift of the closure element does provide a point at which a reliable set pressure measurement may be determined, this approach is not an acceptable test procedure in many applications. For example, there may be a relatively noisy environment where the test operator may not be able to detect the "audible pop." Furthermore, in some applications, such as in boiling water reactor plants, there are hazardous radiation environments in which the set point test operator may not safely enter the immediate region of the valve-to-be-tested. In the prior art, there have been attempts to utilize the above described "audible pop" technique with an acoustical transducer so that remote set point testing may be performed for valves in operational systems. However, these attempts have been unsuccessful, principally due to background noise.
It is an object of the present invention to provide a remote set pressure measurement device.
A further object is to provide a set pressure measurement device which may monitor set pressure characteristics of valves in hostile operational environments.
It is yet another object to provide a plurality of set pressure measurement devices coupled to safety valves at remote location which may be operated periodically under the control at a central controller.